The international community has agreed to a set of architectural standards for intermatability of electrical connectors for the telecommunications industry. The connectors that are most commonly used are modular plugs and jacks that facilitate interconnection of electronic data cables, for example.
A plug typically includes a generally rectangular housing having an end section shaped for at least partial insertion into a socket of a corresponding jack. The plug includes a plurality of contact elements electrically connected to the insulated conductors of an electronic data cable. The contact elements extend through the housing so that free ends thereof are arranged in parallel on an outer peripheral surface of the end section of the plug. The other end of the cable may be connected to a telephone handset, for example.
A jack may be mounted to a wall panel, for example, and includes a socket shaped to at least partially receive an end section of a modular plug, and a plurality of insulation displacement contact slots for receiving respective ones of insulated conductors of an electronic data cable. The jack also includes a plurality of contact elements for electrically connecting conductors of the plug to corresponding conductors of the electronic data cable. First of the contacts are arranged in parallel as spring finger contacts in the socket. The spring finger contacts resiliently bearing against corresponding contact elements of the modular plug when it is inserted in the socket in the above-described manner. Second ends of the contact elements include insulation displacement contacts that open into respective ones of the insulation displacement contact slots. Each insulation displacement contact is formed from contact element which is bifurcated so as to define two opposed contact portions separated by a slot into which an insulated conductor may be pressed so that edges of the contact portions engage and displace the insulation such that the contact portions resiliently engage, and make electrical connection with, the conductor. The two opposed contact portions of the insulation displacement contacts are laid open in corresponding insulation displacement contact slots. As such, an end portion of an insulated conductor can be electrically connected to an insulation displacement contact by pressing the end portion of the conductor into an insulation displacement contact slot.
The above-mentioned electronic data cables typically consist of a number of twisted pairs of insulated copper conductors held together in a common insulating jacket. Each twisted pair of conductors is used to carry a single stream of information. The two conductors are twisted together, at a certain twist rate, so that any external electromagnetic fields tend to influence the two conductors equally, thus a twisted pair is able to reduce crosstalk caused by electromagnetic coupling.
The arrangement of insulated conductors in twisted pairs may be useful in reducing the effects of crosstalk in data cables. However, at high data transmission rates, the wire paths within the connector jacks become antennae that both broadcast and receive electromagnetic radiation. Signal coupling, ie crosstalk, between different pairs of wire paths in the jack is a source of interference that degrades the ability to process incoming signals.
The wire paths of the jack are arranged in pairs, each carrying data signals of corresponding twisted pairs of the data cable. Cross talk can be induced between adjacent pairs where they are arranged closely together. The cross talk is primarily due to capacitive and inductive couplings between adjacent conductors. Since the extent of the cross talk is a function of the frequency of the signal on a pair, the magnitude of the cross talk is logarithmically increased as the frequency increases. For reasons of economy, convenience and standardisation, it is desirable to extend the utility of the connector plugs and jacks by using them at higher data rates. The higher the data rate, the greater difficulty of the problem. These problems are compounded because of international standards that assign the wire pairs to specified terminals.
Terminal wiring assignments for modular plugs and jacks are specified in ANSI/EIA/TIA-568-1991 which is the Commercial Building Telecommunications Wiring Standard. This Standard associates individual wire-pairs with specific terminals for an 8-position, telecommunications outlet (T568B). The pair assignment leads to difficulties when high frequency signals are present on the wire pairs. For example, the wire pair 3 straddles wire pair 1, as viewed looking into the socket of the jack. Where the electrical paths of the jack are arranged in parallel and are in the same approximate plane, there is electrical crosstalk between pairs 1 and 3. Many electrical connectors that receive modular plugs are configured that way, and although the amount of crosstalk between pairs 1 and 3 is insignificant in the audio frequency band, it is unacceptably high at frequencies above 1 MHz. Still, it is desirable to use modular plugs and jacks of this type at these higher frequencies because of connection convenience and cost.
U.S. Pat. No. 5,299,956 teaches cancellation of the cross talk arising in the jack using capacitance formed on the circuit board which is connected to the jack. U.S. Pat. No. 5,186,647 teaches of the reduction of cross talk in an electrical connector by crossing over the paths of certain contact elements in the electrical connector. While these approaches to reducing cross talk may be useful, they may not be sufficient to satisfy the ANSI/TIA/EIA-568-B.2-1 standard for Gigabit Ethernet (the so-called “Category 6” cabling standard). This standard defines much more stringent conditions for crosstalk along the cable than that defined in ANSI/TIA/EIA-568-A for Category 5 cable. The high-frequency operation demanded from the Category 6 standard also produces problems for the connectors and jacks used to connect any two Category 6 cables.
Traditionally, capacitors contain dielectric material that separates two electrically conductive plates. In most cases, this material has a higher dielectric constant than air which allows capacitors using these materials to be much smaller than if air separated the plates alone. The dielectric material has previously exotic or expensive. The cost of the dielectric material may increase the cost of manufacturing capacitors.
Capacitors obtained from external sources can often have severe limitations, or have large margins of error. As such, they may not be suitable for high-accuracy applications. If accurate capacitance is required, then an alternate method of providing the capacitance may be necessary.
It is generally desirable to overcome or ameliorate one or more of the above mentioned difficulties, or at least provide a useful alternative.